In leisure vehicles such as a motorcycle, an all terrain vehicle, or a personal watercraft, communication devices built into the vehicle are typically coupled to each other through serial communication lines. The serial communication lines increase in number as the communication devices mounted in the vehicle increase in number, causing a diameter of wiring harness to increase. In addition, it is necessary to equip a new communication line to incorporate a new communication device into the leisure vehicle. This results in a need for re-design of the harness and makes it difficult to improve system extensibility. For the purpose of reducing harness wires and improving the system extensibility, Japanese Laid-Open Patent Application Publication No. Sho. 61-66436 discloses a configuration in which a front controller disposed in a front side of a vehicle body of a motorcycle is coupled to a rear controller disposed under a seat through a multiplex transmission line and communication devices built into the vehicle body perform multiplexed data communication through the multiplex transmission line.
However, in the configuration disclosed in Japanese Laid-Open Patent Application Publication No. Sho. 61-66436, because wiring of the multiplex communication line is not specially devised, an electromagnetic wave noise is likely to enter the multiplex transmission line if in-vehicle noise sources such as a battery, a regulator, etc, are disposed in the vicinity of the multiplex transmission line, thus making it difficult to improve communication stability. Since multiplex communication is performed in such a manner that data is communicated between plural communication devices through one multiplex transmission line unlike in normal serial communication, entry of the noise may adversely affect plural communications.